Fiber optic cables include one or more optical fibers or other optical waveguides that conduct optical signals, for example carrying voice, data, video, or other information. In a typical cable arrangement, optical fibers are placed in a tubular assembly. A tube may be disposed inside an outer jacket or may form the outer jacket. In either case, the tube typically provides at least some level of protection for the fibers contained therein. Optical fibers are ordinarily susceptible to damage from water and physical stress.
Without an adequate barrier, moisture may migrate into a fiber optic cable and weaken or destroy the cable's optical fibers. Without sufficient physical protection, stress or shock associated with handling the fiber optic cable may transfer to the optical fibers, causing breakage or stress-induced signal attenuation.
One conventional technique for protecting the optical fibers from damage is to fill the cable with a fluid, a gel, a grease, or a thixotropic material that strives to block moisture incursion and to absorb mechanical shock. Such fluids and gels are typically messy and difficult to process, not only in a manufacturing environment but also during field service operations. Field personnel often perform intricate and expensive procedures to clean such conventional materials from optical fibers in preparation for splicing, termination, or some other procedure. Any residual gel or fluid can render a splice or termination inoperably defective, for example compromising physical or optical performance.
Another conventional technology for protecting optical fibers entails placing a water absorbent chemical, such as water-swellable material, within the cable. The chemical absorbs water that may inadvertently enter the cable, and swells to prevent the water from traveling down long lengths of cable and degrading the delicate optical fibers. In one conventional approach, particles of the water absorbent chemical are mixed with the gel discussed above, and the mixture is inserted into the cable. This approach typically suffers from the same drawbacks as using a pure form of a gel; gels and related materials are messy and difficult to process.
In another conventional approach, a water-swellable chemical is applied to the surface of a tape or a yarn that is inserted in the cable lengthwise. If water enters the cable, the water-swellable chemical interacts with the water and swells to impede and stop water flow lengthwise along the cable. However, conventional tape and yarn technologies typically offer limited protection against incursions of seawater. The salt content of seawater typically reduces the effectiveness of water-swellable chemicals via interfering with the interaction between the seawater and the chemicals.
In many instances, a manufacturer will label a fiber optic cable seawater resistant if the cable can pass a test involving subjecting the cable to a three percent seawater mixture. In such tests, typically three percent of the solution is seawater and the remaining ninety-seven percent is distilled water. Since natural seawater has a salinity of between about three percent and about five percent, such tests provide a salinity of only about 0.09 percent (3% seawater multiplied by 3% salinity equals 0.09% net salinity) and a corresponding specific gravity of only about 1.004.
Withstanding seawater having a three percent salinity is significantly more challenging than withstanding a three percent seawater solution. In an actual field deployment, a fiber optic cable may need to withstand the full, three-to-five percent salinity of seawater. Otherwise, the fiber optic cable may have an increased risk of failure.
In additional to lacking adequate saltwater performance, conventional fiber optic cable technology often fails to provide a sufficient density of optical fibers or a desirable level of fiber loading capacity. Conventional cables containing large number of optical fibers typically have diameters that are too large. In other words, users often want a conventional cable of a given diameter to contain more optical fibers than are available with conventional cable designs. Additionally, high fiber-count cables often are heavy and can be cumbersome in terms of field access, installation, and preparation.
One type of conventional fiber optic ribbon cable employs a very large central loose tube design, wherein all optical fibers are located in one central buffer tube with strength rods and jacket material placed outside the central tube. Optical fiber ribbons are stacked inside the buffer tube, typically with a maximum capacity of 864 optical fibers, such as 24 ribbons of 36 fibers each. One drawback of this cable design is that to achieve high fiber capacities, the central buffer tube becomes very large, resulting in excessive space between the fiber optic ribbons and the inner wall of the buffer tube. Conventional dry, water-swellable materials struggle to achieve adequate water blocking in this large annular space. In a typical approach, the space is filled with gel. However, the required quantity of gel increases the weight of the cable thereby encumbering the installation process. Moreover, the gel tends to be messy and craftsman unfriendly.
In another conventional approach, a fiber optic cable includes multiple buffer tubes stranded about a central strength rod with a jacket applied over the buffer tubes and the strength rod. Each buffer tube carries a group of optical fibers, with a typical fiber capacity of 144 optical fibers (12 ribbons of 12 fibers each) in each buffer tube, yielding a cable of 864 optical fibers. In conventional stranded buffer tube designs, the buffer tubes are typically gel filled for water blocking. One drawback in such conventional cable designs is that achieving higher fiber capacities involves increasing the diameters of the buffer tubes and thereby increasing the overall cable diameter. Further, the gel filling inside the buffer tubes contributes to the cable's weight. Heavy, gel-filled cables are generally more difficult to install, and the gel is messy.
Accordingly, to address these representative deficiencies in the art, an improved capability is needed for protecting optical fibers from water damage. Further need exists for a fiber optic cable that can protect ribbons of optical fibers from seawater or saltwater. A need further exists for a fiber optic cable that can restrict the flow of any saltwater or seawater that might inadvertently enter the cable, to avoid lengthwise progression of unwanted saltwater or seawater. Dry water blocking technology is needed for high-count fiber optic cables, including high-density ribbon cables. Need exists for compact cable designs that can accommodate numbers of optical fibers in a relatively small diameter.
A capability addressing one or more of the aforementioned needs, or some related need in the art, would provide robust fiber optic installments and would promote optical fibers for communications and other applications.